This invention relates generally to methods and apparatus for computed tomographic (CT) imaging of an object, and more particularly to method and apparatus for reducing artifacts and increasing spatial resolution at high scan rates in sampling rate limited CT imaging systems.
To avoid view aliasing artifacts, data-sampling rates must be increased proportionately for faster CT scan speeds. As an example, if a data acquisition system (DAS) sampling rate is sufficient at 984 Hz for a 1.0 second scan speed, the DAS sampling rate must be at least 984/x for a CT scanner that rotates at x seconds per revolution. Accordingly, the DAS sampling rate must be at least 1968 Hz for a 0.5 second scan speed. In one known scanning system, the DAS sampling rate is limited to 1408 Hz. For a fixed number of projections, the sampling density in the azimuthal direction decreases with an increase in distance from an iso-center. Thus, at 0.5 second scan speeds, this is a view deficiency in such systems caused by a lack of adequate samples in an azimuthal direction. This view deficiency results in aliasing artifacts and reduced spatial resolution.
There is therefore provided, in one aspect, a method for reducing aliasing artifacts in a computed tomography system. The method includes scanning an object with a computed tomography system to acquire a projection data set of measured views; synthesizing additional views of the projection data set utilizing view interpolation; and filtering and backprojecting the projection data set utilizing a weighting function dependent upon parameters Rƒ and Rt, where radius Rƒ around an isocenter of the CT imaging system is selected in accordance with a low artifact criterion and Rt is a parameter defining a transition region outside of radius Rƒ around the isocenter of the CT imaging system.
In another aspect, a method for reducing aliasing artifacts in a computed tomography system is provided that includes scanning an object with a computed tomography (CT) imaging system to acquire a projection data set of measured views; reconstructing a first image utilizing the measured views to produce an image having a central, essentially artifact-free zone; interpolating views between measured views to produce a projection data set having interpolated views; reconstructing a second image utilizing the interpolated views; and producing a blended image from the first image and the second image utilizing a weighting function selected to smoothly transition from the first image to the second image in a transition region surrounding an isocenter of the CT imaging system.
In still another aspect, there is provided a computed tomographic (CT) imaging system having a rotating gantry, a detector array on the rotating gantry, and a radiation source on the rotating gantry configured to project a beam of radiation towards the detector array through an object to be imaged. The system is configured to scan an object to acquire a projection data set of measured views; synthesize additional views of the projection data set utilizing view interpolation; and filter and backproject the projection data set utilizing a weighting function dependent upon parameters Rƒ and Rt, where radius Rƒ around an isocenter of the CT imaging system is selected in accordance with a low artifact criterion and Rt is a parameter defining a transition region outside of radius Rƒ around the isocenter of the CT imaging system.
In yet another aspect, there is provided a computed tomographic (CT) imaging system having a rotating gantry, a detector array on the rotating gantry, and a radiation source on the rotating gantry configured to project a beam of radiation towards the detector array through an object to be imaged. The system is configured to scan an object to acquire a projection data set of measured views; reconstruct a first image utilizing the projection data set of measured views to produce an image having a central, essentially artifact-free zone; interpolate views between measured views of the projection data set of measured views to produce a projection data set having interpolated views; reconstruct a second image utilizing the interpolated views; and produce a blended image from the first image and the second image utilizing a weighting function selected to smoothly transition from the first image to the second image in a transition region surrounding an isocenter of the CT imaging system.
In still another aspect, there is provided a computer configured to read a projection data set of measured views obtained by scanning an object with a computed tomographic (CT) imaging system; synthesize additional views of the projection data set utilizing view interpolation; and filter and backproject the projection data set utilizing a weighting function dependent upon parameters Rƒ and Rt, where radius Rƒ around an isocenter of the CT imaging system is selected in accordance with a low artifact criterion and Rt is a parameter defining a transition region outside of radius Rƒ around the isocenter of the CT imaging system.
In yet another aspect, there is provided a computer readable medium having recorded thereon instructions configured to read a projection data set of measured views obtained by scanning an object with a computed tomographic imaging system; reconstruct a first image utilizing the projection data set of measured views to produce an image having a central, essentially artifact-free zone; interpolate views between measured views to produce a projection data set having interpolated views; reconstruct a second image utilizing the interpolated views; and produce a blended image from the first image and the second image utilizing a weighting function selected to smoothly transition from the first image to the second image in a transition region surrounding an isocenter of the CT imaging system.
It will be observed that embodiments of the present invention result in reduced aliasing artifacts and increased spatial resolution for scan rates that would otherwise require increased data acquisition system sampling rates.